The present invention relates generally to engine control systems for internal combustion engines, and more particularly to a method and apparatus for characterizing an air mass flow rate target.
In general, internal combustion engines have at least one inlet manifold for supplying air or a combustible mixture of air and fuel to the engine combustion spaces. To increase the charge of combustible mixture that is supplied to the combustion spaces of the engine, it is common to employ pressurized induction systems, such as superchargers and turbochargers, which increase the amount of air delivered to the combustion spaces of the engine. Since fuel is metered to the engine as a function of the mass of air delivered to the combustion spaces, the amount of fuel delivered to the combustion spaces is also increased so as to maintain proper air/fuel ratio. As such, various performance aspects of the engine, such as power output and/or efficiency, can be improved over normally aspirated induction systems.
Turbochargers are a well known type of pressurized induction system. Turbochargers include a turbine, which is driven by exhaust gas from the engine, and a compressor, which is mechanically connected to and driven by the compressor. Rotation of the compressor typically compresses intake air which is thereafter delivered to the intake manifold. The pressure differential between the compressed air and the intake manifold air is known as turbo boost pressure.
At various times during the operation of the engine, it is highly desirable to increase, reduce or eliminate turbo boost pressure. This reduction is typically implemented by controlling the amount of exhaust gas provided to the turbocharger. One common method for controlling the amount of exhaust gas delivered to the turbocharger is a wastegate valve, which is employed to bypass a desired portion of the exhaust gas around the turbine. Most automotive turbochargers use a wastegate valve to control the amount of exhaust gas supplied to the turbine blades. By controlling the amount of exhaust gas that is bypassed around the turbine, the turbo boost pressure and the pressure in the intake manifold can be controlled. Therefore, it is important to determine how much exhaust gas must be bypassed for a given operating condition. If too much exhaust gas is bypassed, not enough power will be produced. Conversely, if not enough exhaust gas is bypassed, engine damage may occur due to an overboost condition.
Methods for controlling the wastegate are well known in the industry. Conventional systems attempt to control the boost pressure by xe2x80x9cbleeding offxe2x80x9d gas as boost pressure becomes too high. However, these conventional pressure-based systems are reactionary and have several drawbacks. In particular, control systems now often employ model based fueling methods which are based on air flow characteristics. Because most other fueling models target air flow to determine fuel delivery characteristics, it is also desirable to target air flow for engines having pressurized induction systems.
Accordingly, it is an object of the present invention to provide a method for controlling a wastegate which overcomes the shortcomings of the conventional pressure-based systems.
In one embodiment, the present invention provides a method for characterizing an air mass flow rate target within an internal combustion engine. The method includes determining a reference air mass flow rate term. In addition, a predicted compressibility term is determined. The reference air mass flow rate term and the predicted compressibility term are processed to determine an air mass flow rate target.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.